We absolutely loved being in the Galapagos Islands and seeing all the iguanas, blue-footed boobies, Galapagos penguins, sea lions, giant tortoises, etc.
One good thing to know is that all your "landings" will be by Zodiacs; some landings are "wet" and some "dry". Be sure to take some Aqua shoes or Tevas for the wet landings. Also, many of the island tours with the Naturalist Guides are extremely difficult; so if you have any disabilities or don't get around well, be sure to ask before you go! AND, keep in mind that there are NO bathroom possibilities on any of the tours, and most of them last 2 1/2 to 3 hours. If you suffer from Urinary Tract problems or incontinence, be forewarned and take along anything that will help you with that; i.e., adult diapers, etc.
These islands are very primitive...that's the whole point in going where most people will never go. It's best to keep that in mind when packing for a trip there. If you are traveling to the Galapagos via cruise ship, your cruise line will send you a list of what to bring; among which will definitely be binoculars, camera(s), insect repellant, sun screen and wide-brimmed hats.
We are in our 60's, and my husband has had a heart attack; but we found all but 2 of the excursions to be relatively easy on us. One was 3 hours long and extremely difficult, as we walked on trails of lava rock, and it was very hilly and the footing was not solid. Bearing all this in mind, if you choose to visit the Galapagos, you will definitely enjoy the experience. Remember to try very hard not to leave your "carbon footprint", as the Galapagos' eco-system is very fragile.